Filters of the type wherein air suction is utilized to force liquid being filtered through a sheet-like filter media have been known and used in the filter art. In these prior art filters as shown, for example, in U.S. Pat. Nos. 3,087,620, 3,347,378, 3,358,834, 3,506,128 and 3,690,466, an elongated sheet of filter media, such as a thick filter paper, was supported on a chain linked conveyor located with a tank. To enhance the flow of liquid through the media some means for producing a vacuum below the media was provided. One serious problem which arose with such filters was in providing adequate air sealing along the sides and ends of the media. Without proper sealing the power required for producing an adequate suction or vacuum in the collection tank under the conveyor became excessive, or the flow produced through the filter media was inadequate due to air leakage. The sealing problem was further aggravated when it became necessary to advance the filter media as it became loaded or clogged with filtrate. The problem of maintaining an adequate vacuum in the collection tank was also related to the problem of providing a conveyor support for the media that was movable, yet perforated to the degree necessary to allow the suction force to take effect and cause liquid to flow through the media.
Other problems with such filter apparatus arose in providing an efficient means for introducing fresh filter media as the media being used became clogged and also for precoating the fresh media. In addition, it was found necessary or highly desirable to provide some means for removing excessive air from the fluid being filtered and also of removing liquid from and/or drying relatively thick filter cakes or filtrate accumulations. Further, it was desired to provide a filter apparatus that would operate at least semi-automatically without the necessity for being closely monitored.
Accordingly, a general object of the present invention is to provide an improved filter apparatus that solves the aforesaid problems.
Another more specific object of the invention is to provide a filter apparatus of the vacuum type wherein an elongated sheet or filter media forms the bottom of a receiving tank and is immersed in the liquid being filtered and is effectively sealed along both sides and the ends of the tank so that a vacuum produced in a chamber below the tank will cause a relatively high flow rate through the media.
Another object of the present invention is to provide a filter apparatus wherein an elongated filter media is supported on an inclined, continuous conveyor means that not only provides the necessary support with flexibility but also has a high porosity to facilitate adequate flow as well as strength and durability.
Another object of the present invention is to provide a filter apparatus wherein an elongated filter media is supported on a continuous conveyor that is advanced automatically at a speed that varies in response to variations in the pressure differential above and below the filter media, which variations are directly related to variations in the dirt load on the media.
Another object of the present invention is to provide a filter apparatus with an endless conveyor that is automatically controlled to advance the media under full and operating differential pressure and which permits modulation of media speed in response to variations in dirt load as signified by the differential pressure.
Another object of the present invention is to provide a filter apparatus wherein an elongated filter media forming the bottom of a receiving tank for dirty fluid is supported on a perforated continuous conveyor that is inclined upwardly from a media inlet end of the tank to a media exit end which enables the sheet media to utilize additional cake forming filter media.
Yet another object of the present invention is to provide a filter apparatus of the type wherein an elongated strip of filter media is supported on and moved by a continuous conveyor means defining a pervious wall between a receiving tank for dirty liquid and a collector tank for filtered liquid, and further to provide an adequate sealing means around the periphery of said receiving tank so that unfiltered dirty fluid cannot migrate into said collector tank.
Another object of the present invention is to provide a filter apparatus of the type wherein an elongated strip of filter media is supported on and moved by a continuous conveyor means which also provides a means for drying, dewatering and/or compressing the filter cake or the filter media at the front end of the filter.
Still another object of the present invention is to provide a filter apparatus of the type wherein an elongated strip of filter media is supported on and moved by a continuous conveyor means that is particularly easy to operate and maintain and that is particularly well adapted for ease and economy of manufacture.